Antenna of ionized air



A08- 2l, 1956 c. c. LASTER, JR 2,760,055-

ANTENNA OF IONIZED AIR BY AM.

ATTORNEY Aug. 21, 1956 C. C. LASTER, JR

ANTENNA 0F IONIZED AIR 2 sheds-sheet 2 Filed Aug. 20, 1952.

INVENTOR Za/reime Isedi.;

BY hm ATTORNEY United States Patent O ANTENNA or IoNIzED AIR Clarence C. Laster, Jr., Burlington, N. C., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application August 20, 1952, Serial No. 305,336

24 Claims. (Cl. Z50-1) This invention relates to antennas, and more particularly to ionized air antennas provided with wave length and automatic directional controls.

In the transmitting or receiving of electrical wave energy, it has been necessary to provide antennas consisting of a visible network of physical wires and rods of predetermined xed sizes with complicated supporting structures of high masts and towers.

An object of this invention is to provide simple invisible antennas composed of ionized columns of air produced by streams of X-rays or radioactive emanations of radiant energy to eliminate the use of rod and wire antennas and their supporting towers.

Another object is the provision of control means for producing, focusing, and aiming columns of ionized air in predetermined controlled directions and combinations to transmit and/or receive electrical wave energy in radio detection and ranging.

Another object is to control and Vary the effective wave length of the ionized air antennas to match the frequency of the transmitted or received electrical wave energy.

Still another object is to provide two ionized air column antennas from a single X-ray tube and predetermine their directions relative to each other.

With these and other objects in view, the present invention comprises an X-ray tube or source of radioactive emanations for producing ionized columns of air of desired wave lengths in predetermined angular relationship, with means for focusing and aiming them in selected directions for optimum operating characteristics by automatically controlling the movement of the tube or radioactive substance through electronic control of an actuating selsyn unit.

Other objects and advantages of the invention will be apparent from the following detailed description when considered in conjunction with the accompanying drawings, wherein:

Fig. l is a diagrammatic view of an X-ray tube with means for producing and focusing two ionized air column antennas in predetermined V angular relationship, control means for varying and determining their effective antenna or wave length, and means for aiming the ionized air antennas in selected directions for achieving optimum operating results by automatic control of the movement of the X-ray tube through electronic control of an actuating selsyn unit;

Fig. 2 is a front elevational view of a dual target X- ray tube for producing two focused ionized air antennas extending in predetermined directions, which tube may be connected and controlled in a manner similar to that shown in Fig. l;

Fig. 3 is a front elevational View, partly in section, of a radioactive source for producing an ionized air antenna with means for aiming it and also showing electrical connections therefrom to a high frequency receiver and/or transmitter;

Fig. 4 shows an electrically connected stationary X- Patented Aug. 2l, 1956 ray tube with means for rotating the target within the tube to provide a collimated stream of rotating X-rays to produce a moving ionized air antenna, and

Fig. 5 discloses an X-ray tube provided with a window of electrically conductive glass connected to an electrical device for receiving and/ or transmitting electrical energy through the ionized air antenna produced by this tube.

Referring now to the drawings, attention is first directed to Fig. l which illustrates a preferred embodiment of the invention wherein an X-ray tube for producing ionized air antennas is mounted in bearings 11-12 for controlled rotation by a selsyn unit 13. The X-ray tube 10 may be constructed like the well-known low pressure Coolidge tube where a concave cathode 15 of tungsten is heated to incandescence by an electrical circuit. In the present invention the tube 10 is provided with external slip rings 16-17 and contacting brushes 18-19 to establish an electrical heating circuit to the cathode 15. A heavy tungsten target or anti-cathode 20 of the tube has two especially designed contoured faces 21 and 22 for producing and focusing two main streams of X- rays 24 and 25 produced by electrons from the cathode 15 striking the dual targets 21-22. These beams of X- rays Z4, 25 are further focused and directed by slits or windows 26, 27 in a lead collimator 2S secured to the outside surface of the envelope of the tube. Thus a V antenna 24-25 is obtained with good directional characteristics.

The target 20 of the rotatable X-ray tube is electrically connected to a high direct current potential through a slip ring 30 and a contacting stationary brush 31. The entire tube 10 is rotated by the selsyn unit 13 consisting of a master motor 32 and a slave motor 33. In the selsyn system two shafts, not mechanically coupled, are adapted to rotate at the same speed with a definite synchronism between them for every instant of time. If the shafts are to be stationary, this simply means that when one shaft is set at a definite position the other shaft will take up this predetermined corresponding set position. Thus the shaft of the slave motor 33 secured to the X-ray tube 10 may be set in any desired position by an electronic control to the master motor 32 to aim the X-ray bearns 24, 25 in a controlled direction.

Electrical power for operating the X-ray tube is obtained from an alternating current source 35 (Fig. l) which is connected in series with the primary of a variable transformer 36. The secondary of this variable transformer is connected through Kenetron or hot cathode tubes 37-38 and inductances 39-40 to the stationary brushes 31 and 19, respectively, of the X-ray tube 10. The Kenetron tubes are capable of rectifying voltages exceeding 100,000 volts to supply a direct current to the leads of the X-ray tube. An adjustable lead 41 of the secondary of the transformer 36 is connected to the stationary brush 18 of the X-ray tube to supply a heating current to the concave cathode 15 thereof.

A voltmeter 42 is connected across the brushes 31 and 19 to measure the direct current voltage being supplied to the X-ray tube 10, and a grounded inductance coil 43 is connected to the brush 31 to prevent the high frequency signals from passing into ground.

Hence by operating the controls on the variable transformer 36 the voltage across the X-ray tube is controlled to vary the effective length of the ionized columns of air produced by the beams 2.4-25 so that the length of the columns of this V antenna approach the wave length of the transmitted or received signals.

Received high frequency signals from a transmitter are conducted along the ionized columns of air 24-25 and pass through a supporting rod 45 therefor, through the slip ring 30, brush 31, conductor 46, through a low frequency blocking condenser to a tuned high frequency tank circuit 51. The received signal then passes into the receiver 52. The signal is also detected and rectified by a rectifying tube 53. This rectified signal is applied to a high frequency filter comprising a first high frequency by pass capacitor 54, a resistor 55, and a second high frequency by pass capacitor 56. This rectified and filtered signal voltage is then applied to an output resistor 57 and a low frequency blocking filter including a resistor 58 and an adjustable capacitor 59. The voltage appearing across the capacitor 59 is a direct voltage that is propoi-tional to the strength of the incoming signal. From here this voltage is directed through conductors 61-62 to a sensitive relay 64. When the received signal reaches a predetermined optimum strength, the voltage is then sufficiently high to operate the sensitive relay 64. The operated relay 64 in turn closes a circuit to actuate a power relay 65 which opens contacts 66 to disconnect power from the master motor 32 of the selsyn unit 13, thereby stopping the rotation of the X-ray tube lib and positioning the V antenna 24-25 in the precise direction to obtain a desired predetermined signal strength. Also in this system the wave length of the antenna can be adjusted to a desired value and the selsyn unit controlled to stop the rotation of the antenna when signals of that particular wave length are received.

In place of the X-ray tube 10 using a single target 20 having two contoured faces 21--22, another X-ray tube 70 having two separate targets 71-72 (Fig. 2) arranged in any desired positions may be substituted in the system shown in Fig. 1 to provide a dipole antenna.

Fig. 3 discloses another embodiment of the invention in which a radioactive substance 73, such as radium, uranium, salts of radium, thorium, actinium, radioactive carbon, etc., is mounted at the end of a bore 74 in a long lead cylinder 75, which is pivotally and rotatably mounted by means of a V shaped member 76 on a swivel base 77. The lead cylinder is electrically insulated from the V shaped member by insulation 73. A handle 79 is provided on the member 76 for aiming the cylinder 75 in a desired direction. Radioactive emanations pass from the open end of this bore 74 to ionize and render conductive a long column of air 80 which acts as an antenna in transmitting and receiving electric signals to and from a high frequency transmitter and receiver 81.

Another embodiment for producing ionized air antennas is shown in Fig. 4, wherein a self-rectifying X-ray tube 83 has its target 84 rotated by a rotor 85 of a motor whose armature 86 is outside the envelope of the X-ray tube. Power is supplied to the target 84 from a transformer 87 through a brush 88 and a contact ring 89 attached to the rod supporting the target and rotor 85. A lead collimator 90 with a circumferential slit 9'1 for directing and controlling the width of the ionized air beam antenna 92 is provided on the outside of the X-ray tube 83. Spaced conducting rings 82. are mounted in .the slit 91 and insulated from the collimator by insulation 95. Here signals are received or transmitted over the ionized air antennas 92, through the conducting rings 82 and a conductor `93 to a high frequency receiver and/or transmitter 81.

Instead of having the signals sent through the target of the X-ray tube and out over the ionized air beam antenna, the signals may be transmitted to the ionized air antenna through a Window 94 of electrically conductive glass sealed into and made a part of the envelope of the X-ray tube as shown in Fig. 5.

It is to be understood that the above described embodiments are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art i which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

l. In a system for signalling by electromagnetic waves, an X-ray tube having a cathode and a target electrode for producing an invisible antenna of ionized air, means to apply an adjustable voltage between said cathode and said target electrode to vary the length of the ionized air antenna, said target electrode being of such configuration that a well defined beam of X-rays is produced therefrom, said X-rays being directed into the atmosphere to ionize a column o-f atmospheric air, means for rotating the target electrode and the ionized air antenna, means for controlling the said rotation to automatically stop and retain the ionized air antenna in a desired position when a predetermined strength of said electromagnetic waves is applied to said antenna, a high frequency circuit, and means to connect said circuit to said antenna of ionized air.

2. In a system for signalling by electromagnetic waves, an X-ray tube having a cathode and a target electro-de, said target electrode being of such configuration that a well defined beam of X-rays is produced therefrom, said X-rays being directed into the atmosphere to provide an ionized air antenna for receiving signals in the forms of electromagnetic waves, means for providing an adjustable voltage between said target and said cathode for controlling the length of the antenna, a high frequency circuit, means to conduct said electromagnetic waves between said circuit and said ionized air antenna, means for rotating the target electrode to sweep the ionized air antenna through a predetermined path, and means for controlling the rotating means to automatically stop the antenna in a desired position when the antenna is receiving the electromagnetic waves at a predetermined strength.

3. In a high frequency signalling system, a high frequency circuit for the signals, an X-ray tube having a cathode and a target electrode within an envelope, said envelope having an electrically-conductive window therein, said target being of such configuration that a well defined beam of X-rays is produced therefrom, said X- rays being directed into the atmosphere through the window of electrically conductive glass in the envelope of the X-ray tube to ionize a column of atmospheric air for use as an antenna, means to apply an adjustable voltage between said cathode and said target electrode tovary the length of the ionized air antenna, and means for connecting the electrically-conductive glass to the high frequency circuit for signals to be transmitted and received through the antenna.

4. A high frequency signal responsive apparatus ineluding a high frequency circuit for the signals, an X-ray tube having a single cathode and two targets, said targets being of such configuration that a pair of well defined beams of X-rays are produced therefrom, said X-rays being directed into the atmosphere to ionize two columns of atmospheric airfor use as antennas, means to apply adjustable voltages between said cathode and said target electrodes to vary the lengths of the antennas, and means for connecting the two targets to the high frequency circuit.

5. A high frequency signal responsive apparatus comprising an X-ray tube for producing an ionized air antenna and having a cathode and a target electrode mounted within an envelope, means to apply an adjustable voltage between said cathode and said target electrode to vary the length of the ionized air antenna, said target electrode being mounted for rotatable movement and being of such configuration that a well defined beam of X-rays is produced therefrom, a collimator mounted on the exterior of the envelope of the X-ray tube and having a circumferential slit, a conducting ring mounted in the said slit in the collimator, means for insulating the ring from the collimator, said target being so constructed and arranged that the beam of X-rays is adapted to pass through the slit and in contact with said conducting ring, a high frequency circuit for the signals, and means for connecting the ring to the high frequency circuit.

6. In a system for signalling by electromagnetic waves, a high frequency means for receiving electrical signals, an ,X-ray tube having a cathode and a target electrode,

means to apply an adjustable voltage between said cathode and said target electrode, said target electrode being of such configuration that a well defined beam of X-rays is produced therefrom, said X-rays being directed into the atmosphere to ionize a column of the atmospheric air to produce an ionized air antenna, the length of the antenna being varied by said adjustable voltage applying means, means for connecting the receiving means to the ionized air antenna, a selsyn unit for rotating the target electrode, and means controlled by the electromagnetic waves received on the ionized air antenna for auto-matically stopping the rotation of said target electrode when said waves are at a predetermined level.

7. In a high frequency signal responsive apparatus, a high frequency circuit for the signals, an X-ray tube having an electron-emitting cathode and an X-ray-emitting target, a portion of said target being within the path of said emitted electrons so that X-rays are produced when said emitted electrons strike said target, said portion being of such configuration that said emitted X-rays are formed into a sharply dened beam, said beam being adapted to enter and ionize the atmosphere to form a column of ionized air for use as an antenna, an adjustable source of voltage connected across said cathode and said target, means to vary said source to vary the length of the ionized air antenna, a selsyn unit for rotating the X-ray tube to sweep the antenna in a circular path, and control means interconnecting the antenna and high frequency circuit and the selsyn unit to stop rotation of the X-ray tube when an optimum of selectivity for the apparatus is obtained.

8. In a high frequency signal responsive apparatus, an X-ray tube for producing an invisible antenna of ionized air, said X-ray tube having a cathode and a target electrode, means to apply an adjustable voltage between said cathode and said target electrode to vary the length of the ionized air antenna, said target electrode being of such configuration that a well defined beam of X-rays is produced therefrom, said X-rays being directed into the atmosphere to ionize a column of atmospheric air, a high frequency circuit, and means to connect said circuit to said column of ionized air.

9. In a system for signalling by electromagnetic waves, an X-ray tube having an electron-emitting cathode and an X-ray emitting target electrode, said target electrode being of such construction that a sharply defined beam of X-rays is produced therefrom when electrons from the cathode impinge thereon and is directed into the atrnosphere to ionize a column of air for use as an antenna, means to apply a voltage across said cathode and target electrode, means to vary said voltage applying means to vary the length of the antenna of ionized air in accordance with the frequency of said electromagnetic waves, a high frequency circuit, and means to electrically connect said circuit to said column of ionized air to conduct s-aid electromagnetic waves thereover.

10. A high frequency signalling system comprising an X-ray tube having an electron-emitting cathode and an X-ray-emitting target, a portion of said target being within the path of said emitted electrons so that X-rays are produced when said emitted electrons strike said target, said portion being of such configuration that said emitted X-rays are formed into a sharply dened beam, said beam being adapted to enter and ionize the atmosphere to form a column of ionized air for use as an antenna, means to apply an adjustable voltage across said cathode and said target to vary the length of said antenna, a high frequency electrical circuit, and means to connect said high frequency circuit to said antenna of ionized air.

11. In a high frequency signalling apparatus, an X-ray tube having an electron-emitting cathode and an X-rayemitting target, said target being mounted axially of said tube and a portion thereof being in the path of the electrons emitted from said cathode, said portion being of such construction that a well dened beam of X-rays is fit formed having a path transversely of said axis, Said beam of X-i'ays being adapted to enter and ionize a portion of the air adjacent said tube, said ionized portion of air being in the form of a column and rendered conductive due to ionization to be used as an antenna, means to apply an adjustable voltage between said cathode and said target to vary the length of the ionized air antenna, a high frequency electrical circuit, and means to electrically connect said ionized column of air to said high frequency circuit.

l2, A high frequency signalling system comprising an X-ray tube having an electron-emitting cath-ode and an X-ray-emitting target mounted therein along an axis of said tube, a portion of said target adapted to be in the path of the electrons emitted by said cathode so that X- rays are produced by the electrons striking said target, said portion of said target being of such configuration that a well defined beam of X-rays is produced and adapted to direct the X-rays along a path transversely of said axis, said beam of X-rays adapted to enter and ionize the atmosphere to form a column of ionized air for use as an antenna, means to apply an adjustable voltage across said cathode and said target to vary the length of the antenna, a high frequency circuit, and means to electrically connect said circuit to said column of ionized air.

13. In a high frequency signal responsive apparatus, an X-ray tube, said X-ray tube having a cathode and a target electrode within anenclosure, said target electrode being adapted for rotative movement, means to rotate said target electrode, said target electrode being of such configuration that a well defined beam of X-rays is produced therefrom, said X-rays being directed into the atmosphere to ionize a column of atmospheric air for use as anantenna, means to apply an adjustable voltage between said cathode and said target electrode to vary the length of the ionized air antenna, a high frequency circuit, and means to connect said circuit to said column of ionized air.

14. A high frequency signalling system comprising an X-ray tube having an electron-emitting cathode and an X-ray-emitting target electrode mounted within an enclosure, said target electrode being adapted for rotative movement, means to rotate said target electrode, a portion of said target electrode being within the path of Said emitted electrons so that X-rays are produced when said emitted electrons strike said target electrode, said portion being of such configuration that said emitted X-rays are formed into a sharply defined beam, said beam being adapted to enter and ionize the atmosphere to form a column of ionized air for use as an antenna, means to apply an adjustable voltage across said cathode and saidL target electrode to vary the length of said antenna, a high frequency electrical circuit, and means to connect said circuit to said column of ionized air.

l5. A high frequency signal responsive apparatus cornprising an X-ray tube having an electron-emitting cathode and an X-ray-emitting target within an envelope, said target and said envelope having a common axis, means to rotate said target on said axis, a portion of said target being in the path of the electrons emitted from said cathode, said portion being of such construction that a sharply defined beam of X-rays is formed having a path transversely of said axis, said beam of X-rays being adapted to enter and ionize a portion of the air adjacent said tube, said ionized portion of air being in the form of a column and rendered conductive due to ionization to be used as an antenna, means to apply a variable v-oltage between said cathode and said target to vary the length of said antenna, a high frequency electrical circuit, and means to electrically conect said ionized column of air to said high frequency circuit.

16. In a high frequency circuit for signalling by electromagnetic waves, a rotatably mounted X-ray tube having an electron-emitting cathode and an X-ray-emitting target electrode mounted within the tube, said target electrode being of such construction that a sharply defined beam of X-rays is produced therefrom when electrons from the cathode impinge thereon and directed into the atmosphere to ionize a column of air for use as an antenna, means to apply a voltage across said cathode and target electrode, means to vary said voltageapplying means to vary the length of the column of ionized air in accordance with the frequency o-f the electromagnetic waves, a motor unit to rotate said X-ray tube and the antenna formed thereby, an input circuit including a source of power to drive said motor, relay means connected in said input circuit between said power source and said motor unit, and means interconnecting said high frequency circuit, said ionized air antenna, and said relay means adapted to operate said relay means when said electromagnetic waves are at a predetermined level to stop the rotation of said X-ray tube and said antenna by said motor.

17. A high frequency signalling system comprising an X-ray tube having an electron-emitting cathode and an X-ray-emitting target mounted therein along an axis of said tube, adjustable means to apply a diiference of potential between said cathode and said target, a portion of said target adapted to be in the path of the electrons emitted by said cathode so that X-rays are produced by the electrons striking said target, said portion of said target being of such configuration that a pair of wel] defined beams of X-rays are produced and adapted to direct the X-rays along paths transversely of said axis, said paths of said beams of X-rays defining an acute angle, said beams of X-rays adapted to enter and ionize the atmosphere to form two columns of ionized air for use as a V antenna, a high frequency circuit, and means to electrically connect said circuit to said columns of ionized air.

18. In a high frequency system for signalling by electromaguetic waves, a rotatably-mounted X-ray tube having an electron-emitting cathode and an X-ray-emitting target mounted therein along an aXis of said tube, a motor to rotate the tube about said axis, an input circuit including a source of power to drive said motor, adjustable means to apply a difference of potential between said cathode and said target, a portion of said target adapted to be in the path of the electrons emitted by said cathode so that X-rays are produced by the electrons striking said target, said portion of said target being of such configuration that a pair of well defined beams of X-rays are produced and adapted to direct the X-rays along paths transversely of said axis, said beams of X-rays adapted to enter and ionize the atmosphere to form two columns of ionized air for use as an antenna which is rotated by said motor rotating said tube, a relay connected in said input circuit between said power source and said motor, a high frequency circuit, means to convey said electromagnetic waves from the ionized air antenna to said high frequency circuit, and means connected to said conveying means to operate said relay and thereby stop the rotation of said tube and antenna by said motor when said electromagnetic waves are at a predetermined level.

19. In a high frequency signalling system, an X-ray tube having an electron-emitting cathode and two X-rayemitting targets, a portion of each target being within the path of said emitted electrons so that X-rays are produced when said emitted electrons strike said targets, said portions being of such configuration that said emitted X-rays are formed into two sharply defined beams, said beams being adapted to enter and ionize the atmosphere to form two columns of ionized air for use as a dipole antenna, means to apply an adjustable voltage across said cathode and said targets to vary the length of the antenna, a high frequency circuit, and means to electrically connect said high frequency circuit to said targets and hence to said columns of ionized air.

20. A high frequency signalling system comprising an X-ray tube having an electron-emitting cathode and a pair of X-ray-emitting targets, said cathode being mounted along an axis of the tube and said targets being mounted symmetrically about said axis, adjustable means to apply a difference of potential between said cathode and said targets, a portion of each target adapted to be in the path of the electrons emitted by said cathode so that X-rays are produced by the electrons striking said targets, said portions of said targets being of such configuration that two well defined beams of X-rays are produced and directed along paths transversely of said axis, said beams of X-rays adapted to enter and ionize the atmosphere to form two columns of ionized air for use as a dipole antenna, a high frequency circuit, and means to electrically connect said circuit to the columns of ionized air.

2l. In a high frequency signal responsive apparatus, an X-ray tube for producing an invisible sweeping antenna of ionized air, said X-ray tube having a cathode and a target electrode, means to apply an adjustable voltage between said cathode and said target electrode to vary the length of the ionized air antenna, said target electrode being of such configuration that a Well defined beam of X-rays is produced therefrom, said X-rays being directed into the atmosphere to ionize a column of atmospheric air to form the antenna, means to rotate said target electrode withinsaid tube to sweep the antenna, a high frequency circuit, and means to connect said circuit to the ionized air antenna.

22. A high frequency signalling system comprising an X-ray tube having an electron-emitting cathode and an X-ray-emitting target, said target being rotatably mounted axially of said tube, means to rotate said target, a portion of said target being in the path of electrons emitted from said cathode, said portion being of such construction that a well defined beam of X-rays is formed having a path transversely of said axis, said beam of X-rays being adapted to enter and ionize a portion of the air adjacent said tube, said ionized portion of air being in the form of a column and rendered conductive due to ionization to be used as a rotating antenna, means to apply an adjustable voltage between said cathode and said target to vary the length of the ionized air antenna, a high frequency electrical circuit, and means to electrically connect the ionized column of air to said high frequency circuit.

23. A high frequency signalling lsystem comprising an X-ray tube having an electron-emitting cathode and an X-ray-emitting target mounted Within an envelope, a section of said envelope being made of electrical-lyconductive glass, a portion of said target being within the path of said emitted electrons so that X-rays are produced when said emitted electrons strike said target, said portion being of such configuration that said emitted X-rays are formed into a sharply dened beam, said beam being adapted to pass through said section of electrically-conductive glass and enter and ionize the atmosphere to form a column of ionized air for use as an antenna, means to apply an adjustable voltage across said cathode and said target to vary the length of the antenna, a high frequency electrical circuit, and means to connect said high frequency circuit to said section of electricallyconductive glass and hence to the column of ionized air.

24. In a high frequency signalling apparatus, an X- ray tube having an electron-emitting cathode and an X- ray-emitting target within an envelope, a section of said envelope being made of electrically-conductive glass, said target being mounted axially of said envelope and a portion thereof being in the path of the electrons emitted from said cathode, said portion being of such construction that a well defined beam of X-rays is formed having ra path transversely of said axis, said beam of X-rays being adapted to pass through said section of electricallyconductive glass and enter and ionize a portion of the air adjacent said envelope, the ionized portion of air being inthe form of a column and rendered conductive due to ionization to be used as an antenna, means to apply an adjustable voltage between said cathode and said target to vary the length of the ionized air antenna, a high frequency electrical circuit, and means to electrically connect said section of electrically-conductive glass to said high frequency circuit.

References Cited in the le of this patent UNITED STATES PATENTS Hettinger July 8, 1919 Engler Aug. 14, 1925 10 Rave Oct. 16, 1928 Weber et al Feb. 27, 1934 Busignies et a1. Nov. 8, 1941 Higgonet Feb. 10, 1942 Weber Nov. 19, 1946 Deloraine et al Apr. 3, 1951 FOREIGN PATENTS Great Britain Apr. 30, 1948 

